Various kinds of flood lubricated bearings for a rotating shaft are known in which the shaft loading is sustained by a bearing pad or shoe in contact with the shaft through an intervening oil film. The present invention is related to improvements in these shaft load-bearing elements, overcoming problems of distortion and other damages which can occur with previous bearings unless special, careful handling is provided.
For many years it has been common practice to use steel backed, babbitted thrust bearings to carry the axial load in large rotary machines such as steam driven turbine-generator sets. More recently, to overcome problems of extreme temperatures, copper-backed babbitted bearing plates and shoes have been used. With its greatly superior thermal conductivity, the use of copper has reduced substantially the peak temperatures developed in the babbitt during machine operation.
Unfortunately, copper is a relatively soft material and thrust plates, bearing shoes, and so forth manufactured according to this technique have been prone to warpage even while in storage. Furthermore, these copper backed parts have been particularly susceptible to damage during handling and shipping. These problems have become more acute over the years as a trend toward larger machines has necessitated the use of correspondingly larger bearings. For example, in a large steam turbine of current vintage, thrust bearings may be on the order of three feet in diameter.
One solution, for minimizing distortion in pivoted thrust shoes, has been to use a higher strength copper alloy such as chromium-copper. However, even this has not been entirely successful and has increased the bearing cost considerably.
Another potential solution to the problem, particularly for thrust bearings, is exemplified by the pad construction disclosed by U.S. Pat. No. 3,829,180 in which a graphite-fiber composite material is applied to a steel backing plate. The facing material is said to insulate the bearing pad from oil-shear heat and to thereby reduce the tendency toward distortion. However, such tilting pad construction has not found utility in large rotating machinery such as steam turbine-generator sets.
Accordingly, it is an object of the present invention to provide a load-bearing element for a flood lubricated bearing which is rugged, free from long term distortion acquired during storage, substantially free from damage acquired during handling, and which avoids the elevated temperature problems inherent in steel backed load-bearing parts.